Implantable medical devices, materials and structures sometimes require post-implant access. For example, tissue expanders used in reconstruction surgeries require highly accurate location of at least one predetermined access point under the skin. After locating a predetermined access point, the caregiver typically passes a syringe needle through the skin at the access point in order to access the tissue expander's insufflation port. Some implanted structures may have complex geometries and/or access locations may move or deform over time. Conversely, some implants can include a simple device geometry where it can be difficult to detect the exact access location (e.g., due to very small angular changes in and around the access location). Even when an access point is determined, location accuracy though thick tissue associated with high Body Mass Index (BMI) patients can adversely affect the ability to safely access the implant. Some locator devices include conventional magnet locators that generally include magnets with locator holes. However, precise vertical alignment of the magnet and access hole can be difficult to achieve, especially for patients with a high BMI. Further, some catheters and other medical devices and applications can include two or more hidden spots that must be precisely located. For example, in various medical applications including research there can be a need for a device which can precisely locate a device with more than two subcutaneous ports.
Thus, there is a need for a device which is sufficiently sensitive for patients with very thick tissue. The device would preferably precisely, accurately and concurrently locate a plurality of spots on or under skin without requiring a hole in the locator magnet. The would preferably not require a magnet dedicated to each target and not require any magnet to align over the physical perimeter of the target or targets.